Method of forming an electrically conductive, freestanding microporous polymer sheet

ABSTRACT

A freestanding, microporous polymer sheet ( 52, 56 ) is composed of a polymer matrix binding an electrically conductive matrix. The polymer matrix preferably includes UHMWPE, and the electrically conductive matrix is preferably in powder form. The UHMWPE is of a molecular weight that provides sufficient molecular chain entanglement to form a sheet with freestanding characteristics. Multiple microporous sheets ( 30 ) can be wound or stacked in a package filled with an electrolyte to function as electrodes in an energy storage device ( 86 ), such as a battery. Metallic layers ( 81, 83 ) can be applied to the microporous sheets to function as current collectors in such devices.

RELATED APPLICATIONS

[0001] This application is a division of U.S. patent application Ser.No. 09/507,174, filed Feb. 18, 2000, which claims priority from U.S.Provisional Patent Application No. 60/120,842, filed Feb. 19, 1999.

TECHNICAL FIELD

[0002] This invention relates to the formation of an electricallyconductive, freestanding microporous polymer sheet and, in particular,to such a sheet for use in the manufacture of energy storage and othersuitable devices.

BACKGROUND OF THE INVENTION

[0003] The following background information is presented by way ofexample with reference to the manufacture of electrodes used in energystorage devices. Descriptions of the construction details of energystorage devices relevant to the present invention are set forth in DavidLinden (Editor in Chief), Handbook of Batteries, 2^(nd) ed.,McGraw-Hill, Inc. (1995). Electrode preparation for many energy storagedevices begins with the formation of a slurry containing anelectrochemically active material in powder form, a fluoropolymer, andsolvent. The slurry is coated onto a metal foil that acts as a currentcollector. The metal foil coated with the electrochemically activematerial is then passed through a drying oven to remove the solvent. Thefluoropolymer acts as a binder that holds together the electrochemicallyactive material and forms a porous electrode. Often the electrode iscalendered to densify the electrochemically active material coated onthe current collector by increasing the volume or packing fraction ofthe electrochemically active material and thereby reducing the porosityof the electrode. The current collector also functions as a carrier forthe electrochemically active material and the binder because thecombination of the two of them is of insufficient mechanical integrityto stand on its own. The electrode is then cut into ribbons for windingor stacking into a packaged energy storage device.

[0004] Fluoropolymers, such as polyvinylidene fluoride, havehistorically been used as polymer binders because of theirelectrochemical and chemical inactivity in relation to most polymer,gel, or liquid electrolytes. However, it is difficult, if notimpossible, to produce freestanding porous electrodes utilizingfluoropolymers at traditional binder contents (2-10 wt. %) because theirlow molecular weights provide inadequate chain entanglement. Otherbinders such as EPDM rubber and various types of polyethylene can beused, but they also do not provide microporous sheets with freestandingproperties. “Freestanding” refers to a sheet having sufficientmechanical properties that permit manipulation such as winding andunwinding in sheet form for use in an energy storage device assembly.

[0005] A special type of polyethylene, ultrahigh molecular weightpolyethylene (UHMWPE), can be used to make a microporous sheet withfreestanding properties at the binder contents specified above. Therepeat unit of polyethylene is shown below:

(—CH₂CH₂—)_(x),

[0006] where x represents the average number of repeat units in anindividual polymer chain. In the case of polyethylene used in many filmand molded part applications, x equals about 10³-10⁴ whereas for UHMWPEx equals about 10⁵. This difference in the number of repeat units isresponsible for the higher degree of chain entanglement and the uniqueproperties of UHMWPE.

[0007] One such property is the ability of UHMWPE to resist materialflow under its own weight when the UHMWPE is heated above itscrystalline melting point. This phenomenon is a result of the longrelaxation times required for individual chains to slip past oneanother. UHMWPE exhibits excellent chemical and abrasion resistance, andthe hydrocarbon composition of UHMWPE has a much lower skeletal density(0.93 g/cc) than many of the fluoropolymers commonly used in electrodepreparation. Such commonly used fluoropolymers include polyvinylidenefluoride (1.77 g/cc) and polytetrafluoroethylene (2.2 g/cc).

[0008] UHMWPE is commonly used as the polymer matrix or binder forseparators used in lead-acid batteries. Such separators result from theextrusion, calendering, and extraction of mixtures containing UHMWPE,precipitated silica, and processing oil. The resultant separators havemany advantages: high porosity (50-60%), a dentritic growth-inhibitingultrafine pore size, low electrical resistance, good oxidationresistance, and sealability into a pocket configuration. Theseseparators usually contain a silica to UHMWPE weight ratio from about2.5 to about 3.5 or a corresponding volume fraction ratio in the rangeof 1.0 to 1.5. Such separators are designed to prevent electronicconduction (i.e., short circuits) between the anode and cathode whilepermitting ionic conduction via the electrolyte that fills the pores.

[0009] While UHMWPE is an integral part of separator technology, its usein the extrusion and extraction of free-standing, electricallyconductive porous film electrodes has never been achieved. Thisinvention addresses the desire to fabricate such film electrodes for usein energy storage and other electronic device applications.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is, therefore, to provide anelectrically conductive, freestanding microporous polymer sheet formedat a relatively high volume fraction of the electrically conductivematrix (composed of an electrochemically active powder and anelectrically conductive agent, if required) to the polymer matrix andhaving sufficient mechanical properties for use in energy storage andother electronic device applications.

[0011] The present invention is a freestanding, microporous polymersheet that is composed of a polymer matrix binding a materialcomposition (i.e., the electrically conductive matrix) having electricalconductivity properties. The polymer matrix preferably includes UHMWPE,and the material composition preferably is in powder form. The UHMWPE isof a molecular weight that provides sufficient molecular chainentanglement to form a sheet with freestanding characteristics, and thematerial composition powders have relatively small surface areas andsubstantially reduced oil absorption values as compared to precipitatedsilica as used in battery separator technology. The polymer matrix ofthe sheet does not exceed a volume fraction of about 0.20, and thevolume fraction of voids or pores of the polymer sheet is between about0.20 and about 0.80.

[0012] Multiple microporous sheets can be wound or stacked in a packagefilled with an electrolyte to function as electrodes in an energystorage device, such as a battery. Metallic layers can be applied to themicroporous sheets to function as current collectors in such devices.

[0013] In a first preferred embodiment of the invention, thefreestanding, microporous polymer sheet is manufactured by combiningUHMWPE, a material composition in powder form and having electricalconductivity properties, and a plasticizer (e.g., mineral oil). Amixture of UHMWPE and the material composition powder is blended with asufficient quantity of plasticizer and the blend is extruded to form ahomogeneous, cohesive mass. A blown film process or another traditionalcalendering method is used to shape the oil-filled sheets to their finalthicknesses. In an extraction operation similar to that used for theproduction of lead acid battery separators, the oil is removed from thesheets. Metallic layers are then applied to the extracted sheets to formcurrent collectors. A metallic layer can be one of a metal film formedby sputter deposition on, electroless deposition on, electrodepositionon, plasma spraying on, or roll coating of a metal slurry on themicroporous sheet; or a porous or nonporous metal foil laminated to themicroporous sheet. In some cases, sufficient metal powder can beincorporated in the polymer sheet such that a metallic layer asdescribed above is not required.

[0014] In a second preferred embodiment of the invention, a polymermatrix, containing an UHMWPE in an amount and of a molecular weightsufficient to provide the necessary molecular chain entanglement to forma freestanding microporous sheet, binds a material composition havingelectrical conductivity properties. The resulting electricallyconductive sheet is wound or stacked in a package, and the pores of thesheet are filled with an electrolyte and used as one of many electrodesin an energy storage device, for example, a battery, capacitor,supercapacitor, or fuel cell. One of the benefits of this polymer matrixis that it can be used to form, and potentially provide intimate contactbetween adjacent layers of, the anode, cathode, or separator.

[0015] In a third preferred embodiment of the invention, multipleextruders are used to simultaneously produce anode, cathode, andseparator films that are formed in accordance with a continuouscoextrusion process or are laminated together at the end of a continuousprocess. This process promotes an integral, coherent bond betweenadjacent anode, cathode, and separator layers and reduces the risk ofdelamination during extraction. This process also provides intimatecontact between the anode and the separator and between the cathode andthe separator without collapsing porosity at adjacent layer interfaces.The resultant multiple layer ribbon with one or more current collectorsis cut to size, and the pores are filled with electrolyte to produce anenergy storage device.

[0016] Additional objects and advantages of this invention will beapparent from the following detailed description of preferredembodiments thereof which proceeds with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIGS. 1 and 2 are, respectively, a frontal elevation view and anexploded side elevation view of a lead-acid cell assembly formed ofelectrodes made in accordance with the present invention.

[0018]FIG. 3 is a schematic diagram showing a continuous coextrusionprocess for forming the electrode assemblies of this invention.

[0019]FIG. 4 is a cross-sectional view of the electrode assembly of thisinvention.

[0020]FIG. 5 is a cross-sectional view of an electrochemical cellincorporating the electrode assembly of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] The polymeric material preferably used in this invention is anultrahigh molecular weight polyolefin. The polyolefin most preferablyused is an ultrahigh molecular weight polyethylene (UHMWPE) having anintrinsic viscosity of at least 10 deciliter/gram, and preferablygreater than about 14 deciliters/gram. It is not believed that there isan upper limit on intrinsic viscosity for the UHMWPEs usable in thisinvention. Current commercially available UHMWPEs have an upper limit ofintrinsic viscosity of about 29 deciliters/gram.

[0022] The plasticizer employed in the present invention is anonevaporative solvent for the polymer and is preferably a liquid atroom temperature. The plasticizer has little or no solvating effect onthe polymer at room temperature; it performs its solvating action attemperatures at or above the softening temperature of the polymer. ForUHMWPE, the solvating temperature is greater than about 160° C., andpreferably in the range of between about 160° C. and about 220° C. It ispreferred to use a processing oil, such as a paraffinic oil, naphthenicoil, aromatic oil, or a mixture of two or more such oils. Examples ofsuitable processing oils include: oils sold by Shell Oil Company, suchas ShellFlex™ 3681, Gravex™ 41, Catnex™ 945; and oils sold by Chevron,such as Chevron 500R; and oils sold by Lyondell, such as Tufflo™ 6056.

[0023] Any solvent for extracting the processing oil from the individualfilms or multiple layer film may be used in the extraction process, solong as the solvent is not deleterious to the electrode activeingredients contained in the polymer matrix and has a boiling point thatmakes it practical to separate the solvent from the plasticizer bydistillation. Such solvents include 1,1,2 trichloroethylene,perchloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane,1,1,2-trichloroethane, methylene chloride, chloroform,1,1,2-trichloro-1,2,2-trifluoroethane, isopropyl alcohol, diethyl ether,acetone, hexane, heptane, and toluene.

[0024] In some cases, it is desirable to select the processing oil suchthat any residual oil in the polymer sheet after extraction iselectrochemically inactive.

[0025] A first preferred embodiment of the present invention is use ofthe freestanding microporous film as a composition. The terms “film” and“sheet” are used interchangeably throughout this patent application todescribe products made in accordance with the invention, and the term“web” is used to encompass films and sheets. The practice of theinvention is not limited to a specific web thickness. The presentinvention forms a freestanding microporous polymer sheet, which ismanufactured by combining an UHMWPE, an electrochemically active powderand an electrically conductive agent (e.g., carbon black), if required,with sufficient plasticizer at an appropriate temperature to allowformation of a homogeneous, cohesive sheet. The electrochemically activepowders used to form these sheets vary widely. Some examples are asfollows:

EXAMPLE 1 Production of a Zinc-Containing Sheet

[0026] UHMWPE (1900 HCM; Montell Polyolefins, 2.1 g) was added to zincpowder (<10 μm particle size; Aldrich Chemical Co., 56.0 g) in a 250 mlplastic beaker. The powders were blended with a spatula until ahomogeneous mixture formed, at which time ShellFlex™ 3681 process oil(Shell Oil Co., 9.2 g) was added. The oil-containing mixture was stirreduntil a free-flowing state was achieved, and then the mixture was placedinto a HAAKE Rheomix 600 miniature intensive mixer fitted with rollerblades and driven by a HAAKE Rheocord 90 torque Rheometer, turning at 80RPM and set at 180° C. Additional oil (8.0 g) was added to the mixingchamber. The resultant mixture was compounded for five minutes,resulting in a homogeneous, cohesive mass, This mass was transferred toa C. W. Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15rpm and set at 150° C. The roll gap was adjusted to about 0.7 mm, andthe resulting polymer sheet was removed from the rolls with a take-offknife.

[0027] The sheet was allowed to cool to room temperature, and then arazor blade was used to cut 40 mm×60 mm specimens from the sheet. Thespecimens were next placed in a 500 ml trichloroethylene bath in which amagnetic stir bar was used to circulate the solvent, thereby promotingextraction of the ShellFlex™ 3681 oil. This procedure was repeated threetimes with fresh trichloroethylene to ensure that the oil was fullyextracted from the specimens. The trichloroethylene-laden specimens weredried in a fume hood for five minutes at 20° C., followed by 15 minutesat 90° C. in a forced air oven.

[0028] The resultant porous sheet having a 0.66 mm thickness was weighedand measured to determine its density. A density of 2.91 g/cc wasrecorded, and porosity of 49.4% was calculated from the skeletaldensities of the respective phases.

[0029] The following three Comparative Examples A, B, and C demonstratethe impact of UHMWPE in the successful production of a freestandingmicroporous polymer sheet, such as the sheet described in Example 1.

COMPARATIVE EXAMPLE A

[0030] Polyvinylidene fluoride (Kynar 461; Elf-Atochem, 7.5 g) was addedto zinc powder (<10 μm particle size; Aldrich Chemical Co., 104.3 g) ina 250 ml plastic beaker. The powders were blended with a spatula until ahomogeneous mixture formed, at which time dibutyl phthalate (DBP)(Aldrich Chemical Co., 15.0 g) was added. The DBP-containing mixture wasstirred until a free-flowing state was achieved, and then the mixturewas placed in a HAAKE Rheomix 600 miniature intensive mixer fitted withroller blades and driven by a HAAKE Rheocord 90 torque Rheometer,turning at 80 RPM and set at 160° C. Additional DBP (21.6 g) was addedto the miniature intensive mixer. The resultant mixture was compoundedfor 5 minutes, resulting in a low viscosity, oily mixture that was nottransferable to the C. W. Brabender Prep-Mill two-roll mill. A cohesivesheet was never achieved, even though the mixture contained the samevolume fractions of polymer, zinc, and oil as outlined in Example 1.

COMPARATIVE EXAMPLE B

[0031] Using the same procedure as outlined in Comparative Example A, amixture containing zinc powder (<10 μm particle size; Aldrich ChemicalCo., 104.3 g), polyvinylidene fluoride (Kynar 461; Elf-Atochem, 7.5 g),and dibutyl phthalate (DBP) (Aldrich Chemical Co., 18.3 g) was preparedin the HAAKE Rheomix 600 miniature intensive mixer at 160° C. Theresultant mixture was compounded for 5 minutes, resulting in a pastethat was not transferable to the C. W. Brabender Prep-Mill two-rollmill. A cohesive sheet was not achieved, even though this formulationcontained 18.3 g less dibutyl phthalate than (i.e., one-half of) thatcontained in the formulation of Comparative Example A.

COMPARATIVE EXAMPLE C

[0032] Using the same procedure as outlined in Comparative Example A, amixture containing zinc powder (<10 μm particle size; Aldrich ChemicalCo., 104.3 g), polyvinylidene fluoride (Kynar 461; Elf-Atochem, 9.0 g),and dibutyl phthalate (DBP) (Aldrich Chemical Co., 18.3 g) was preparedin the HAAKE Rheomix 600 miniature intensive mixer at 160° C. and thentransferred to the Brabender Prep-Mill two-roll mill, turning at 15 rpmand set at 135° C. A cohesive sheet was not achieved, even though thisformulation contained 1.5 g more polyvinylidene fluoride than thatcontained in the formulation of Comparative Example B.

EXAMPLE 2 Production of a Nickel-Containing Sheet

[0033] UHMWPE (1900 HCM; Montell Polyolefins, 2.64 g) was added tonickel powder (3 μm particle size; Aldrich Chemical Co., 56.0 g) in a250 ml plastic beaker. The powders were blended with a spatula until ahomogeneous mixture formed, at which time ShellFlex™ 3681 process oil(Shell Oil Co., 12.0 g) was added. The oil-containing mixture wasstirred until a free-flowing state was achieved, and then the mixturewas placed into a HAAKE Rheomix 600, miniature intensive mixer fittedwith roller blades and driven by a HAAKE Rheocord 90 torque Rheometer,turning at 80 RPM and set at 180° C. Additional oil (8.0 g) was added tothe mixing chamber. The resultant mixture was compounded for fiveminutes, resulting in a homogeneous, cohesive mass. This mass wastransferred to a C. W. Brabender Prep-Mill Model PM-300, two-roll mill,turning at 15 rpm and set at 150° C. The roll gap was adjusted to about0.4 mm, and the resulting polymer sheet was removed from the rolls witha take-off knife.

[0034] The oil-filled sheet was extracted as outlined in Example 1.

[0035] The resultant porous sheet having a 0.37 mm thickness was weighedand measured to determine its density. A density of 2.12 g/cc wasrecorded, and porosity of 67.0% was calculated from the skeletaldensities of the respective phases.

EXAMPLE 3 Production of a Graphite-Containing Sheet

[0036] UHMWPE (1900 H; Montell Polyolefins, 10.0 g) and conductivecarbon black (Super P; MMM Carbon, 5.0 g) were added to graphite powder(BG-35; Superior Graphite Co., 85.0 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 20.0 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed into a HAAKE Rheomix 600large intensive mixer fitted with roller blades and driven by a HAAKERheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (80.0 g) was added to the mixing chamber. The resultantmixture was compounded for five minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 150° C. Theroll gap was adjusted to about 1.2 mm, and the resulting polymer sheetwas removed from the rolls with a take-off knife.

[0037] The oil-filled sheet was extracted as outlined in Example 1.

[0038] The resultant porous sheet having a 1.2 mm thickness was weighedand measured to determine its density. A density of 1.12 g/cc wasrecorded, and porosity of 42.5% was calculated from the skeletaldensities of the respective phases.

EXAMPLE 4 Production of a Granulated Carbon-Containing Sheet

[0039] UHMWPE (1900 HCM; Montell Polyolefins, 1.0 g) was added togranulated carbon powder (ENSACO 350; MMM Carbon, 10.0 g having asurface area of about 800 m²/g) in a 250 ml plastic beaker. The powderswere blended with a spatula until a homogeneous mixture formed, at whichtime ShellFlex™ 3681 process oil (Shell Oil Co., 25.0 g) was added. Theoil-containing mixture was stirred until a free-flowing state wasachieved, and then the mixture was placed into a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (13.4 g) was added to the mixing chamber. The resultantmixture was compounded for five minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 150° C. Theroll gap was adjusted to about 0.3 mm, and the resulting polymer sheetwas removed from the rolls with a take-off knife.

[0040] The oil-filled sheet was extracted as outlined in Example 1.

[0041] The resultant porous sheet having a 0.29 mm thickness was weighedand measured to determine its density, which was recorded as 0.41 g/cc.

EXAMPLE 5 Production of an Activated Carbon-Containing Sheet

[0042] UHMWPE (1900 HCM; Montell Polyolefins, 1.0 g) was added toactivated carbon powder (Norit SX Ultra; NORIT Americas Inc., 10.0 ghaving a surface area of about 1150 m²/g) in a 250 ml plastic beaker.The powders were blended with a spatula until a homogeneous mixtureformed, at which time ShellFlex™ 3681 process oil (Shell Oil Co., 12.0g) was added. The oil-containing mixture was stirred until afree-flowing state was achieved, and then the mixture was placed into aHAAKE Rheomix 600 miniature intensive mixer fitted with roller bladesand driven by a HAAKE Rheocord 90 torque Rheometer, turning at 80 RPMand set at 180° C. Additional oil (6.9 g) was added to the mixingchamber. The resultant mixture was compounded for five minutes,resulting in a homogeneous, cohesive mass. This mass was transferred toa C. W. Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15rpm and set at 150° C. The roll gap was adjusted to about 0.3 mm, andthe resulting polymer sheet was removed from the rolls with a take-offknife.

[0043] The oil-filled sheet was extracted as outlined in Example 1.

[0044] The resultant porous sheet having a 0.30 mm thickness was weighedand measured to determine its density, which was recorded as 0.43 g/cc.

EXAMPLE 6

[0045] Production of a Lithium Cobalt Oxide-Containing Sheet

[0046] UHMWPE (1900 HCM; Montell Polyolefins, 9.4 g) and graphite powder(BG-35, Superior Graphite Co., 8.7 g) were added to lithium cobalt oxidepowder (OMG Americas Inc., 81.9 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 15.0 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed into a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (12.0 g) was added to the mixing chamber. The resultantmixture was compounded for five minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 170° C. Theroll gap was adjusted to about 0.4 mm, and the resulting polymer sheetwas removed from the rolls with a take-off knife.

[0047] The oil-filled sheet was extracted as outlined in Example 1.

[0048] The resultant porous sheet having a 0.36 mm thickness was weighedand measured to determine its density. A density of 1.75 g/cc wasrecorded, and a porosity of 47.8% was calculated from the skeletaldensities of the respective phases.

EXAMPLE 7 Production of a Lithium Manganese Oxide-Containing Sheet

[0049] UHMWPE (1900 HCM; Montell Polyolefins, 4.9 g) and conductivecarbon black (Super P; MMM Carbon, 6.3 g) were added to lithiummanganese oxide powder (Japan Energy Corp., 73.8 g) in a 250 ml plasticbeaker. The powders were blended with a spatula until a homogeneousmixture formed, at which time Tufflo process oil 6056 (LyondellLubricants, 24.2 g) was added. The oil-containing mixture was stirreduntil a free-flowing state was achieved, and then the mixture was placedin a HAAKE Rheomix 600 miniature intensive mixer fitted with rollerblades and driven by a HAAKE Rheocord 90 torque Rheometer, turning at 80RPM and set at 180° C. Additional oil (6.0 g) was added to the mixingchamber. The resultant mixture was compounded for 5 minutes, resultingin a homogeneous, cohesive mass. This mass was transferred to a C. W.Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15 rpm andset at 150° C. The roll gap was adjusted to about 0.3 mm, and a sheetwas removed from the rolls with the take-off knife.

[0050] The oil-filled sheet was extracted as outlined in Example 1.

[0051] The resultant porous sheet having a 0.30 mm thickness was weighedand measured to determine its density, which was recorded as 1.50 g/cc.

EXAMPLE 8 Production of a Manganese Dioxide-Containing Sheet

[0052] UHMWPE (1900 HCM; Montell Polyolefins, 2.6 g) and graphite powder(BG-35, Superior Graphite Co., 4.0 g) were added to manganese dioxidepowder (alkaline battery grade; Kerr-McGee Chemical LLC., 32.0 g) in a250 ml plastic beaker. The powders were blended with a spatula until ahomogeneous mixture formed, at which time ShellFlex™ 3681 process oil(Shell Oil Co., 8.0 g) was added. The oil-containing mixture was stirreduntil a free-flowing state was achieved, and then the mixture was placedinto a HAAKE Rheomix 600 miniature intensive mixer fitted with rollerblades and driven by a HAAKE Rheocord 90 torque Rheometer, turning at 80RPM and set at 180° C. Additional oil (12.0 g) was added to the mixingchamber. The resultant mixture was compounded for five minutes,resulting in a homogeneous, cohesive mass. This mass was transferred toa C. W. Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15rpm and set at 150° C. The roll gap was adjusted to about 0.4 mm, andthe resulting polymer sheet was removed from the rolls with a take-offknife.

[0053] The oil-filled sheet was extracted as outlined in Example 1.

[0054] The resultant porous sheet having a 0.39 mm thickness was weighedand measured to determine its density, which was recorded as 1.27 g/cc.

EXAMPLE 9 Production of a Lead (II, III)-Oxide Containing Sheet

[0055] UHMWPE (1900 HCM; Montell Polyolefins, 3.2 g) was added to lead(II, III) oxide powder (Pb₃O₄; 1-2 μm; Aldrich Chemical, 145.8 g) in a250 ml plastic beaker. The powders were blended with a spatula until ahomogeneous mixture formed, at which time ShellFlex™ 3681 process oil(Shell Oil Co. 1.5 g) was added. The oil-containing mixture was stirreduntil a free-flowing state was achieved, and then the mixture was placedin a HAAKE Rheomix 600 miniature intensive mixer fitted with rollerblades and driven by a HAAKE Rheocord 90 torque Rheometer, turning at 80RPM and set at 180° C. Additional oil (22.8 g) was added to the mixingchamber. The resultant mixture was compounded for 5 minutes, resultingin a homogeneous, cohesive mass. This mass was transferred to a C. W.Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15 rpm andset at 150° C. The roll gap was adjusted to about 0.7 mm, and a sheetwas removed from the rolls with the take-off knife after lowering theroll temperature to 130° C.

[0056] The oil-filled sheet was extracted as outlined in Example 1.

[0057] The resultant porous sheet having a 0.67 mm thickness was weighedand measured to determine its density, which was recorded as 3.93 g/cc.

EXAMPLE 10 Production of a Lead (II)-Oxide Containing Sheet

[0058] UHMWPE (1900 HCM; Montell Polyolefins, 1.4 g), barium sulfate(BaSO₄; Aldrich Chemical, 2.1 g), and conductive carbon black (Super P;MMM Carbon, 0.2 g) were added to lead (II) oxide powder (PbO; AldrichChemical, 88.7 g) in a 250 ml plastic beaker. The powders were blendedwith a spatula until a homogeneous mixture formed, at which timeShellFlex™ 3681 process oil (Shell Oil Co., 1.0 g) was added. Theoil-containing mixture was stirred to a free-flowing state was achieved,and then the mixture was placed in a HAAKE Rheomix 600 miniatureintensive mixer fitted with roller blades and driven by a HAAKE Rheocord90 torque Rheometer, turning at 80 RPM and set at 180° C. Additional oil(11.0 g) was added to the mixing chamber. The resultant mixture wascompounded for 5 minutes, resulting in a homogeneous, cohesive mass.This mass was transferred to a C. W. Brabender Prep-Mill Model PM-300,two-roll mill, turning at 15 rpm and set at 150° C. The roll gap wasadjusted to about 0.8 mm, and a sheet was removed from the rolls withthe take-off knife after lowering the roll temperature to 130° C.

[0059] The oil-filled sheet was extracted as outlined in Example 1.

[0060] The resultant porous sheet having a 0.86 mm thickness was weighedand measured to determine its density, which was recorded as 4.06 g/cc.

EXAMPLE 11 Production of a Nickel Hydroxide-Containing Sheet

[0061] UHMWPE (1900 HCM; Montell Polyolefins, 1.9 g) and graphite powder(BG-35; Superior Graphite Co., 3.9 g) were added to nickel hydroxidepowder (OMG Americas Inc., 20.7 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 14.8 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed into a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (3.0 g) was added to the mixing chamber. The resultantmixture was compounded for five minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 175° C. Theroll gap was adjusted to about 0.5 mm, and the resulting polymer sheetwas removed from the rolls with a take-off knife.

[0062] The oil-filled sheet was extracted as outlined in Example 1.

[0063] The resultant porous sheet having a 0.52 mm thickness was weighedand measured to determine its density, which was recorded as 0.87 g/cc.

EXAMPLE 12 Production of a Graphite-Containing Sheet

[0064] UHMWPE (1900 HCM; Montell Polyolefins, 2.1 g) and conductivecarbon black (Super P; MMM Carbon, 1.7 g) were added to graphite powder(BG-35; Superior Graphite Co., 46.1 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 15.0 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed into a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (10.9 g) was added to the mixing chamber. The resultantmixture was compounded for five minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 150° C. Theroll gap was adjusted to about 0.6 mm, and the resulting polymer sheetwas removed from the rolls with a take-off knife.

[0065] The oil-filled sheet was extracted as outlined in Example 1.

[0066] The resultant porous sheet having a 0.58 mm thickness was weighedand measured to determine its density. A density of 0.88 g/cc wasrecorded, and porosity of 58.2% was calculated from the skeletaldensities of the respective phases.

EXAMPLE 13 Production of a Graphite-Containing Sheet

[0067] Example 13 uses the formulation described in Example 12, with theexception that the polymer matrix in this formulation is composed in a3:1 weight ratio of UHMWPE and HDPE in the production of agraphite/conductive carbon black electrode. Using the same procedure asoutlined in Example 12, a porous sheet was formed from a mixturecontaining graphite powder (BG-35; Superior Graphite Co., 46.1 g),conductive carbon black (Super P; MMM Carbon, 1.7 g), UHMWPE (1900 HCM;Montell Polyolefins, 1.6 g), high density polyethylene (HDPE) (1288;Fina Chemical, 0.5 g), and ShellFlex™ 3681 process oil (25.9 g). In thiscase, the oil-filled sheet was removed from the two-roll mill at 135° C.After extraction, the porous sheet had a thickness of 0.25 mm and adensity of 0.90 g/cc.

EXAMPLE 14 Production of a Graphite-Containing Sheet

[0068] Example 14 uses the formulation described in Example 13, with theexception that the polymer matrix in this formulation is composed ofequal amounts of UHMWPE and HDPE in the production of agraphite/conductive carbon black electrode. Using the same procedure asoutlined in Example 12, a porous sheet was formed from a mixturecontaining graphite powder (BG-35; Superior Graphite Co., 46.1 g),conductive carbon black (Super P; MMM Carbon, 1.7 g), UHMWPE (1900 HCM;Montell Polyolefins, 1.05 g), high density polyethylene (HDPE) (1288;Fina Chemical, 1.05 g), and ShellFlex™ 3681 process oil (25.9 g). Inthis case, the oil-filled sheet was removed from the two-roll mill at135° C. After extraction, the porous sheet had a thickness of 0.25 mmand a density of 0.88 g/cc.

[0069] The following two Comparative Examples D and E demonstrate theimpact of the use of UHMWPE in an effective amount in the successfulproduction of a freestanding microporous polymer sheet, such as thatdescribed in Example 14.

COMPARATIVE EXAMPLE D

[0070] Conductive carbon black (Super P; MMM Carbon, 1.7 g), UHMWPE(1900 HCM; Montell Polyolefins, 0.5 g), and high density polyethylene(HDPE) (1288; Fina Chemical, 1.6 g) were added to graphite powder(BG-35; Superior Graphite Co., 46.1 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 15.0 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed in a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (10.9 g) was added to the mixing chamber. The resultantmixture was compounded for 5 minutes, forming a weak paste that was nottransferable to the C. W. Brabender Prep-Mill two-roll mill. A cohesivesheet was never achieved with the low UHMWPE content in thisformulation.

Comparative EXAMPLE E

[0071] Using the same procedure as outlined in Comparative Example D, amixture containing graphite powder (BG-35; Superior Graphite Co., 46.1g), conductive carbon black (Super P; MMM Carbon, 1.7 g), high densitypolyethylene (HDPE) (1288; Fina Chemical, 2.1 g), and ShellFlex™3681process oil (Shell Oil Co., 25.9 g) was prepared in the HAAKE Rheomix600 miniature intensive mixer at 180° C. The resultant mixture wascompounded for 5 minutes, forming a weak paste that was not transferableto the C. W. Brabender Prep-Mill two-roll mill. A cohesive sheet wasnever achieved for this formulation, which contained no UHMWPE.

[0072] Examples 12, 13, and 14 demonstrate that the present inventionencompasses a polymer matrix composed of UHMWPE, either as a solepolymer material or as one of multiple polymer materials, including, butnot limited to, high density polyethylene (HDPE). Table 1 shows,however, that evaluation of the extracted sheets formed in accordancewith Examples 12-14 reveals that the samples produced with higher UHMWPEcontent have better mechanical properties. (Table 1 also shows that nosheet was formed with the lower amounts of UHMWPE used in theComparative Examples D and E.) The data set out in Table 1 were obtainedfrom three samples cut from each sheet into 2.5 cm×7.5 cm strips andevaluated on an Instron machine (Model #4301). All testing was done at acrosshead speed of 50 cm/min. The values reported in Table 1 are averagevalues. TABLE 1 UHMWPE/HDPE Density Modulus Tensile % Strain at ratio(g/cc) (ksi) Strength (psi) Break (%) 100/0  0.88 7.4 344 10.6 75/250.90 4.9 224 9.1 50/50 0.88 3.6 140 6.4 25/75 No Sheet Formed  0/100

EXAMPLE 15 Production of Graphite-Containing Sheet

[0073] UHMWPE (1900 HCM; Montell Polyolefins, 2.1 g), polyvinylidenefluoride copolymer (Kynar 2801; Elf-Atochem, 0.21 g), and conductivecarbon black (Super P; MMM Carbon, 1.7 g), were added to graphite powder(BG-35; Superior Graphite Co., 46.1 g) in a 250 ml plastic beaker. Thepowders were blended with a spatula until a homogeneous mixture formed,at which time ShellFlex™ 3681 process oil (Shell Oil Co., 22.9 g) wasadded. The oil-containing mixture was stirred until a free-flowing statewas achieved, and then the mixture was placed in a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.Additional oil (3.0 g) was added to the mixing chamber. The resultantmixture was compounded for 5 minutes, resulting in a homogeneous,cohesive mass. This mass was transferred to a C. W. Brabender Prep-MillModel PM-300, two-roll mill, turning at 15 rpm and set at 170° C. Theroll gap was adjusted to about 0.3 mm, and a sheet was removed from therolls with the take-off knife after lowering the roll temperature to157° C.

[0074] The oil-filled sheet was extracted as outlined in Example 1.

[0075] The resultant porous sheet having a 0.33 mm thickness was weighedand measured to detennine its density, which was recorded as 0.91 g/cc.

EXAMPLE 16 Production of Graphite-Containing Sheet

[0076] Example 16 uses the formulation described in Example 15, with theexception that this formulation uses a polyvinylidine fluoridehomopolymer. Using the same procedure as outlined in Example 15, aporous sheet was formed from a mixture containing graphite powder(BG-35; Superior Graphite Co., 46.1 g), conductive carbon black (SuperP; MMM Carbon, 1.7 g), polyvinylidene fluoride (Kynar 741; Elf-Atochem,0.21 g), UHMWPE (1900 HCM; Montell Polyolefins, 2.1 g), and ShellFlex™3681 process oil (Shell Oil Co., 25.9 g). After extraction, the poroussheet had a thickness of 0.38 mm and a density of 0.92 g/cc.

EXAMPLE 17 Production of Graphite-Containing Sheet

[0077] Example 17 uses the formulation described in Example 15, with theexception that this formulation includes an additional amount ofpolyvinylidene fluoride copolymer. Using the same procedure as outlinedin Example 15, a porous sheet was formed from a mixture containinggraphite powder (BG-35; Superior Graphite Co., 46.1 g), conductivecarbon black (Super P; MMM Carbon, 1.7 g), polyvinylidene fluoridecopolymer (Kynar 2801; Elf-Atochem, 0.53 g), UHMWPE (1900 HCM; MontellPolyolefins, 2.1 g), and ShellFlex™ 3681 process oil (Shell Oil Co.,25.9 g). After extraction, the porous sheet had a thickness of 0.26 mmand a density of 0.90 g/cc.

EXAMPLE 18 Production of Graphite-Containing Sheet

[0078] Example 18 uses the formulation described in Example 15, with theexception that this formulation substitutes polyacrylonitrile for thepolyvinylidene fluoride copolymer. Using the same procedure as outlinedin Example 15, a porous sheet was formed from a mixture containinggraphite powder (BG-35; Superior Graphite Co., 46.1 g), conductivecarbon black (Super P; MMM Carbon, 1.7 g), polyacrylonitrile (AldrichChemical, 0.21 g), UHMWPE (1900 HCM; Montell Polyolefins, 2.1 g), andShellFlex™ 3681 process oil (Shell Oil Co., 25.9 g). After extraction,the porous sheet had a thickness of 0.36 mm and a density of 0.95 g/cc.

EXAMPLE 19 Production of Graphite-Containing Sheet

[0079] Example 19 uses the formulation described in Example 15, with theexception that this formulation substitutes polyethylene oxide for thepolyvinylidene fluoride copolymer. Using the same procedure as outlinedin Example 15, a porous sheet was formed from a mixture containinggraphite powder (BG-35; Superior Graphite Co., 46.1 g), conductivecarbon black (Super P; MMM Carbon, 1.7 g), polyethylene oxide (PolyoxWSR Coagulant; Union Carbide, 0.21 g), UHMWPE (1900 HCM; MontellPolyolefins, 2.1 g), and ShellFlex™ 3681 process oil (Shell Oil Co.,25.9 g). After extraction, the porous sheet had a thickness of 0.40 mmand a density of 0.93 g/cc.

[0080] A second preferred embodiment of the invention is directed to useof the freestanding microporous polymer sheet in an energy storagedevice. The polymer sheet is especially useful in such devices becauseit is freestanding, porous, electrically conductive, andelectrochemically active. Energy storage devices in which the inventioncan be used include, but are not limited to, capacitors,supercapacitors, batteries, and fuel cells.

[0081] A first preferred implementation of this second preferredembodiment is the use of the freestanding microporous polymer film in abattery. A battery converts chemical energy to electrical energy. A widevariety of electrochemically active materials can be used to form theanode and cathode in batteries as referenced in the Handbook ofBatteries. These materials can include lithium intercalation compoundsincluding lithium nickel oxide, lithium cobalt oxide, and lithiummanganese oxide; lead (II) oxide, lead (II, III) oxide, and mixtures oflead and lead oxide; manganese dioxide; zinc oxide; nickel; zinc; lead;silver; iron; iron oxides; metal hydrides including lanthanum-nickel(LaNi₅); cobalt oxides; hydroxides of nickel, zinc, and cadmium, andcobalt; crystalline or amorphous carbonaceous materials in the form offiber, powder, or microbeads including natural or synthetic graphite,carbon black, coke, mesocarbon microbeads, or activated carbon. Thefollowing examples are illustrative of use of the present invention invarious types of batteries.

EXAMPLE 20 Lead-Acid Secondary Cell

[0082] TABLE 2 Anode Cathode Separator PbO¹, g 88.7 BaSO₄ ², g 2.1Carbon Black³, g 0.2 Pb₃O₄ ⁴, g 145.8 Silica⁵, g 7.0 Colorant⁶, g 0.2Lubricant⁷, g 0.03 Antioxidant⁸, g 0.03 UHMWPE⁹, g 1.4 3.2 2.4 Oil¹⁰, g12 24.3 18.0

[0083] The components of a lead-acid secondary cell manufactured inaccordance with Example 20 are set out in Table 2. FIGS. 1 and 2 showrespective frontal and exploded views of the resultant lead-acid cellassembly. The dry anode ingredients in Table 2 were combined in a 600 mltall form beaker and blended with a spatula. While blending continued,oil (1 g) was added to the mixture. Blending continued until a freeflowing powder formed. The free flowing powder was added to a HAAKERheomix 600 miniature intensive mixer fitted with roller blades anddriven by a HAAKE Rheocord 90 torque Rheometer, turning at 80 RPM andset at 180° C. The remaining oil (11 g) was added to the miniatureintensive mixer. This mixture was compounded for approximately fiveminutes, resulting in a homogeneous, cohesive mass. This mass wastransferred to a C. W. Brabender Prep-Mill Model PM-300, two-roll mill,turning at 15 rpm and set at 150° C. The roll gap was adjusted to about0.67 mm, and a sheet was removed from the rolls with the take-off knife.

[0084] The procedure above was repeated for the cathode formula with thefollowing exceptions: oil (1.5 g) was blended with the dry ingredientsin a 600 ml tall form beaker, additional oil (22.8 g) was added to theminiature intensive mixer, the temperature of the two-roll mill was 130°C., and the gap on the two-roll mill was set to about 0.8 mm.

[0085] The procedure above was repeated for the separator formula withthe following exceptions: oil (12 g) was blended with the dryingredients in a 600 ml tall form beaker, the additional oil (6 g) wasadded to the miniature intensive mixer, the temperature of the two-rollmill was 173° C., and the gap on the two-roll mill was set to about 0.4mm.

[0086] Two rectangles, each measuring 4 cm×6 cm, were cut from both theanode and cathode sheets. One 6 cm×8 cm rectangle was cut from theseparator sheet. Two current collectors, each measuring 4 cm×6 cm, witha 2 cm×10 cm take-off tab, were cut from an expanded lead calcium alloy(0.065 wt. % calcium) strip. The dimensions of the grid wires were 1mm×1 mm, and the dimensions of the grid openings were 8 mm×7 mm.

[0087] One grid was sandwiched between two oil-filled anode sheets, andthe tri-layer assembly was laminated in a Model C Carver LaboratoryPress, at 143° C. and a pressure not greater than 100 kpa. A second gridwas sandwiched between two oil-filled cathode sheets and laminated in aCarver Laboratory Press, at 143° C. and a pressure not greater than 100kPa. The oil-filled separator sheet was sandwiched between the anode andcathode assemblies prepared above and laminated in a Carver LaboratoryPress, at 143° C. and a pressure not greater than 100 kPa. The resultinglaminated cell stack was extracted in a 2.0 liter beaker oftrichloroethylene with a magnetic stir bar turning at 200 rpm. Theextraction was repeated three times with fresh trichloroethylene toensure that the oil was fully extracted. The trichloroethylene-ladencell stack was dried in a fume hood for five minutes at 20° C., followedby 15 minutes at 90° C. in a forced air oven.

[0088] The resultant porous assembly was immersed in a container filledwith 1.05 sp. gr. H₂SO₄. The cell stack and container were placed in avacuum desiccator, which was evacuated to a pressure of 125 mm of Hg forone minute, after which the vacuum was released. This evacuation releasecycle was repeated five times. The cell assembly was removed from thedesiccator and immersed in 600 cc of 1.05 sp. gr. H₂SO₄. The anodecollector tab was connected to the negative lead of a Hewlett PackardModel 6611C DC power supply. The cathode collector tab was connected tothe positive lead. The cell was formed at 0.12 ampere for 23.8 hours.The formation electrolyte (1.05 sp. gr. H₂SO₄) was decanted and replacedwith 1.28 sp. gr. H₂SO₄. The cell received a brief finishing charge,0.12 ampere for 0.25 hour. After a stand time of 0.25 hour, the opencircuit voltage was 2.22 volts. The cell was discharged at 0.3 amp to acut off voltage of 1.75 volts, yielding 0.411 ampere-hour.

EXAMPLE 21 LMO Graphite Secondary Cell

[0089] TABLE 3 Anode Cathode Separator Graphite¹, g 153.6 Carbon Black²,g 5.7 17.9 LMO³, g 210.7 Fumed Silica⁴, g 20.8 UHMWPE⁵, g 7.0 14.0 16.2Oil⁶, g 64.6 69.1 156.9

[0090] The components of a LMO graphite secondary cell manufactured inaccordance with Example 21 are set out in Table 3. The UHMWPE and oil(64.6 g), both listed in the anode formula in Table 3, were blended in a600 ml tall form beaker with a spatula until a slurry formed. Thisslurry was transferred to a HAAKE Rheomix 600 miniature intensive mixerfitted with roller blades and driven by a HAAKE Rheocord 90 torqueRheometer, turning at 80 RPM and set at 180° C. A gel was formed, asindicated by the torque peak, approximately three minutes after theslurry was introduced to the miniature intensive mixer. The remainingdry anode ingredients listed in Table 3 were combined in a 600 ml tallform beaker and blended with a spatula. Approximately five minutes afterthe gellation torque peak, the blended dry anode ingredients were addedto the miniature intensive mixer. This mixture was compounded forapproximately five minutes, resulting in a homogeneous, cohesive mass.

[0091] This mass was transferred to a C. W. Brabender Prep-Mill ModelPM-300, two-roll mill, turning at 15 rpm and set at 175° C. The roll gapwas adjusted to about 0.3 mm, and a sheet was removed from the rollswith the take-off knife. An 8 cm×8 cm square was cut from this anodefilm, placed between aluminum foil cover sheets, transferred to a CarverLaboratory Press, and 143° C. pressed to a thickness of 0.10 mm at apressure of approximately 2,500 kPa. The film was allowed to cool toroom temperature, and the aluminum foil cover sheets were removed.

[0092] The procedure above was followed for the cathode formula listedin Table 3, using UHMWPE (14 g) and oil (69.1 g). In this case, thecathode film from the two-roll mill was pressed to a thickness of 0.15mm, at a pressure of approximately 2,500 kPa in the Carver LaboratoryPress.

[0093] All of the ingredients listed in the separator formula in Table 3were blended in a 600 ml tall form beaker with a spatula until a slurryformed. The slurry was transferred to a HAAKE Rheomix 600 miniatureintensive mixer fitted with roller blades and driven by a HAAKE Rheocord90 torque Rheometer, turning at 80 RPM and set at 180° C. A gel formed,as indicated by the torque peak, approximately three minutes after theslurry was introduced to the miniature intensive mixer. This mixture wascompounded for approximately five minutes, resulting in a homogeneous,cohesive mass. A 0.05 mm separator film was formed from a portion ofthis mass using the two-roll mill, laboratory press, and the techniquedescribed above.

[0094] A 4 cm×6 cm rectangle was cut from both the anode and cathodefilms. A 6 cm×8 cm rectangle was cut from the separator film. A 4 cm×6cm anode collector with a 1.5 cm×6 cm take-off tab was cut from expandedcopper foil, 2Cu6-410F made by Exmet Corporation. This foil was 0.05 mmthick and had a strand thickness of 0.18 mm. A 4 cm×6 cm cathodecollector with a 1.5 cm×6 cm take-off tab was cut from expanded aluminumfoil, 2AL6-40F, made by Exmet Corporation. This foil was 0.05 mm thickand had a strand thickness of 0.18 mm.

[0095] The collectors, oil-filled sheets, and separator were stacked inthe following order: copper collector, anode film, separator, cathodefilm, and aluminum collector. This stack was then laminated in a Model CCarver Laboratory Press, at about 143° C. and at a pressure not greaterthan 100 kPa. The laminated cell stack was extracted in a tall form 600ml beaker of trichloroethylene with a magnetic stir bar turning at 100rpm. This procedure was repeated three times with freshtrichloroethylene to ensure that the oil was fully extracted. Thetrichloroethylene-laden cell stack was dried in a fume hood for fiveminutes at 20° C., followed by 15 minutes at 90° C. in a forced airoven.

[0096] A cell case and slotted cover were fabricated from a 12 mm UHMWPEbillet. The internal cell dimensions were approximately 1 mm×70 mm×100mm. The anode and cathode collector tabs of the extracted, oil-free cellassembly were inserted through the cover slot and fixed in place withepoxy resin so that when the cell cover was in place, the cell assemblytouched the bottom of the cell cavity. The cell assembly, attached cellcover, cell case, a stand, support rod, clamp, 2 cc ground glasssyringe, and 100 mm 20 gauge SS pipetting needle were dried in a forcedair oven at 110° C. for 16 hours.

[0097] Grade 5.0 nitrogen was supplied from 2 H-size gas cylinders to aManostat Model 41-905-000 glove box and air lock via a manifold composedof 6 mm polyflow tubing, two Matheson Model 3102C-580 dual stageregulators, and a Gilmont Model GF-5521-1700 flow meter. The moisturelevel inside the glove box was monitored with a Labcraft digitalhygrometer. A factory sealed one liter flask of EM Industries, Inc.,Selectipur® LP30 (EC:DMC=1:1 w/w, 1M LiPF₆) lithium hexafluorophosphateelectrolyte was placed in the glove box, and the glove box was purgedwith grade 5.0 nitrogen at approximately 16.5 liters per minute for 1hour. This reduced the dew point inside the glove box to −40° C. Thecell assembly, attached cell cover, cell case, stand, support rod,clamp, 2 cc ground glass syringe, and 100 mm 20 gauge SS pipettingneedle were transferred from the forced air oven to the glove box airlock. After 20 minutes the cell assembly, attached cell cover, cellcase, stand, support rod, clamp, 2 cc ground glass syringe, and 100 mm20 gauge SS pipetting needle were transferred from the air lock to theglove box.

[0098] Inside the glove box, the cell case was fixed in an uprightposition by means of the stand, support rod, and clamp. Approximatelyfive milliliters of LP30 electrolyte was transferred to the cell caseusing the syringe and pipetting needle. The cell assembly was insertedinto the cell case. The anode collector tab was connected to thenegative terminal of a Hewlett Packard Model 6611 C DC power supply bymeans of leads passed through glove box wall via gas tight connections.The cathode collector tab was connected to the positive terminal bysimilar means. The power supply voltage limit was set to 4.2 volts, andthe current limit was set to 0.0121 ampere. Over the next hour thenitrogen flow was gradually reduced to 3.2 liters per minute. This wassufficient to maintain the dew point inside the glove box at −40° C.

[0099] The on-charge cell voltage gradually increased to 4.2 volts after3.93 hours. The charging current gradually decreased and charging wasterminated after 8.18 hours, at approximately 0.0005 ampere. The cellwas discharged at 0.0121 ampere for 3.78 hours to a cut off voltage of2.7 volts. The data for the first three charge discharge cycles issummarized in Table 4 below. TABLE 4 Cycle Capacity, mAh RatemA 1stCharge ˜61.6 12.1 1st Discharge 34.7 12.1 2nd Charge ˜45.8 12.1 2ndDischarge 32.3 12.1 3rd Charge ˜29.1 12.1 3rd Discharge 32.9 30.05

EXAMPLE 22 Alkaline Manganese Dioxide Primary Cell

[0100] TABLE 5 Anode Cathode Zinc Dust¹, g 56.0 Manganese Dioxide², g32.0 Graphite³, g 4.0 UHMWPE⁴, g 2.1 2.6 Oil⁵, g 17.2 20.0

[0101] The components of an alkaline manganese dioxide primary cellmanufactured in accordance with Example 22 are set out in Table 5. Thedry anode ingredients in Table 5 were combined in a 600 ml tall formbeaker and blended with a spatula. While blending continued, oil (12 g)was added to the mixture. Blending continued until a free flowing powderwas formed.

[0102] This free flowing powder was added to a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.The remaining oil (5.2 g) was added to the miniature intensive mixer.This mixture was compounded for approximately five minutes, resulting ina homogeneous, cohesive mass. This mass was transferred to a C. W.Brabender Prep-Mill Model PM-300, two-roll mill, turning at 15 rpm andset at 175° C. The roll gap was adjusted to about 0.3 mm, and a sheetwas removed from the rolls with a take-off knife. An 8 cm×8 cm squarewas cut from this anode film, placed between aluminum foil cover sheets,transferred to a Carver Laboratory Press, and 143° C. pressed to athickness of 0.13 mm at a pressure of approximately 2,500 kPa. The filmwas allowed to cool to room temperature, and the aluminum foil coversheets were removed.

[0103] The procedure above was repeated for the cathode formula with thefollowing exceptions: the oil (15 g) was blended with the dryingredients, additional oil (5 g) was added to the miniature intensivemixer, the gap on the two-roll mill was set to about 0.6 mm, and theCarver Laboratory Press was not used.

[0104] Two rectangles, each measuring 4 cm×6 cm, were cut from both theanode and cathode films. One 6 cm×8 cm rectangle was cut from anonwoven, polyamide separator (BG06836; 0.13 mm thick; Hollingsworth &Vose Co.). A 4 cm×6 cm anode collector with a 2 cm×10 cm take-off tabwas cut from expanded copper foil, 2CU6-4/OF made by Exmet Corporation.This foil was 0.05 mm thick and had a strand thickness of 0.18 mm. A 4cm×6 cm cathode collector with a 2 cm×10 cm take-off tab was cut fromexpanded nickel foil, 3Ni4-4-OA, made by Exmet Corporation. This foilwas 0.08 mm thick and had a strand thickness of 0.1 mm.

[0105] The oil-filled sheets, collectors, and separator were stacked inthe following order: anode film, copper collector, separator, nickelcollector and, cathode film. This stack was then laminated in a Model CCarver Laboratory Press, at about 143° C. and at a pressure not greaterthan 100 kPa. This laminated cell stack was extracted in a tall form 600ml beaker of trichloroethylene with a magnetic stir bar turning at 100rpm. This procedure was repeated three times with freshtrichloroethylene to ensure that the oil was fully extracted. Thetrichloroethylene-laden cell stack was dried in a fume hood for fiveminutes at 20° C., followed by 15 minutes at 90° C. in a forced airoven.

[0106] The resultant porous assembly was immersed in a 250 ml specimenjar containing an aqueous solution of 33 wt. % potassium hydroxide andapproximately 0.4 wt. % of a nonionic surfactant, composed of anaromatic polyglycol ether. The cell stack and jar were placed in avacuum desiccator, which was evacuated to a pressure of 125 mm of Hg forone minute, after which the vacuum was released. This evacuation releasecycle was repeated five times. The saturated cell stack was placed in a75 mm×125 mm polyethylene bag so that the current collectors protrudedfrom the bag. The open circuit voltage for this cell was 1.39 volts. Thecell was given a series of 10 minute constant resistance discharges witha one hour rest period between them. The beginning and ending voltagesand currents are summarized in Table 6. TABLE 6 Minutes Ohms VoltsMillamperes 0 1.120 1.39 1.18 10  1.120 1.24 1.11 0 490 1.35 2.49 10 490 1.10 2.29 0 330 1.33 3.39 10  330 0.99 3.00

[0107] A second implementation of this preferred embodiment is the useof the freestanding microporous film in a double-layer (super)capacitor. The following example is illustrative of use of the presentinvention in a double-layer capacitor.

EXAMPLE 23 Carbon Black, Ensaco 350 GR Capacitor

[0108] TABLE 7 Electrode Separator Carbon Black¹, g 11.0 Silica², g 7.0Colorant³, g 0.2 Lubricant⁴, g 0.03 Antioxidant⁵, g 0.03 UHMWPE⁶, g 1.02.4 Oil⁷, g 42.0 18.0

[0109] The components of a carbon black, Ensaco 350 GR capacitormanufactured in accordance with Example 23 are set out in Table 7. Thedry electrode ingredients in Table 7 were combined in a 600 ml tall formbeaker and blended with a spatula. Oil (28 g) was then added to thebeaker while blending with a spatula. Once thoroughly blended, thismixture formed a free flowing powder.

[0110] This free flowing powder was added to a HAAKE Rheomix 600miniature intensive mixer fitted with roller blades and driven by aHAAKE Rheocord 90 torque Rheometer, turning at 80 RPM and set at 180° C.The remaining oil (14 g) was added to the miniature intensive mixer.This mixture was compounded for approximately five minutes, resulting ina homogeneous, cohesive mass. This mass was transferred to a C. W.Brabender Prep-Mill, Model PM-300, two-roll mill, turning at 15 rpm andset at 175° C. The roll gap was adjusted to about 0.4 mm, and a sheetwas removed from the rolls with the take-off knife.

[0111] The procedure above was repeated for the separator formula withthe following exceptions: oil (12 g) was blended with the dryingredients in a 600 ml tall form beaker, additional oil (6 g) was addedto the miniature intensive mixer, the temperature of the two-roll millwas approximately 173° C., and the gap on the two-roll mill was set toabout 0.3 mm. An 8 cm×8 cm square was cut from this separator sheet,placed between aluminum foil cover sheets, transferred to a CarverLaboratory Press, at 143° C., and pressed to a thickness of 0.10 mm at apressure of approximately 2,500 kPa. The film was allowed to cool toroom temperature and the aluminum foil cover sheets were removed.

[0112] Two 4 cm×6 cm rectangles were cut from the electrode sheet. One 6cm×8 cm rectangle was cut from the separator film. Two 4 cm×6 cm currentcollectors with 2 cm×10 cm take-off tabs were cut from expanded titaniumfoil, 2Ti3.5-4/OA made by Exmet Corporation. This foil was 0.05 mm thickand had a strand thickness of 0.09 mm. The collectors, oil-filledsheets, and separator film were stacked in the following order:collector, electrode sheet, separator film, electrode sheet, andcollector. This stack was then laminated in a Model C Carver LaboratoryPress, at about 143° C. and at a pressure not greater than 100 kPa. Thislaminated capacitor assembly was extracted in a tall form 600 ml beakerof trichloroethylene with a magnetic stir bar turning at 100 rpm. Thisprocedure was repeated three times with fresh trichloroethylene toensure that the oil was fully extracted. The trichloroethylene-ladencapacitor was dried in a fume hood for five minutes at 20° C., followedby 15 minutes at 90° C. in a forced air oven.

[0113] The resultant porous capacitor assembly was immersed in a 250 mlspecimen jar containing 1.28 sp. gr. H₂SO₄ electrolyte. The capacitorassembly and jar were placed in a vacuum desiccator, which was evacuatedto a pressure of 125 mm of Hg for one minute, after which the vacuum wasreleased. This evacuation release cycle was repeated five times. Thesaturated capacitor was placed in a 75 mm×125 mm polyethylene bag sothat the current collectors protruded from the bag.

[0114] The capacitor collector tabs were connected to the terminals of aHewlett Packard Model 6611C DC power supply. The power supply voltagelimit was set to 1.2 volts, and the current limit was set to 1 ampere.The initial current was 71 milliamperes, decaying exponentially to 19milliamperes after 10 minutes. After 10 minutes, the power supply wasdisconnected and the open circuit voltage of the capacitor was recorded.The initial open circuit voltage was 0.98 volt, decreasing to 0.65 volt10 minutes after power supply disconnection. Although equipmentnecessary to quantify capacity in farads was unavailable, the behaviorabove is consistent with a functioning capacitor.

[0115] A third preferred embodiment of the invention is a continuouscoextrusion process in which multiple extruders are used tosimultaneously produce a multiple layer film composed of individualanode, cathode, and separator layers. The resultant muliple layer filmwith current collectors is cut to size and filled with electrolyte toproduce an energy storage device. FIG. 3 is a schematic diagramillustrating a continuous coextrusion process for forming the electrodeassemblies of the present invention. The process illustrated employsthree extruders and a coextrusion die.

[0116] An extruder 10 has a metering section containing a feed port 11by means of which a suspension of a polymer in a non-evaporativeplasticizer is fed into the extruder. Extruder 10 has a second meteringsection containing second feed port 111 by means of which an anodeactive material is fed into the second (downstream) metering section.

[0117] An extruder 12 has a metering section containing a feed port 13by means of which a suspension of polymer and filler in a nonevaporativeplasticizer is fed into the extruder. An extruder 14 has a meteringsection containing a feed port 15 by means of which a suspension of apolymer in a nonevaporative plasticizer is fed into the extruder.Extruder 14 has a second metering section containing second feed port115 by means of which a cathode active material is fed into the second(downstream) metering section.

[0118] Extruders 10, 12, and 14 are, preferably, twin screw extrudershaving mixing and conveying sections. The twin screw extruders may havescrews that are either co-rotating or counter-rotating. The temperaturesemployed in the extruders are such as to ensure that the polymer issolvated by the plasticizer, but not so high as to cause degradation ofany component of the slurry composition during its residence time in theextruder. Although twin screw extruders are preferred, other means forapplying heat and shear to the various slurries may be used, such as,for example, a Farrel continuous mixer.

[0119] The anode extrudate is conveyed from extruder 10 to a coextrusiondie 20 via a heated pipe 16; the separator extrudate is conveyed fromextruder 12 to coextrusion die 20 via a heated pipe 17; and the cathodeextrudate is conveyed from extruder 14 to coextrusion die 20 via aheated pipe 18. Melt pumps may be used to feed the extrudates fromextruders 10, 12, and/or 14 to coextrusion die 20.

[0120] Coextrusion die 20 may be either a sheet die or a blown film die.If a blown film is formed, its tubular construction may be slit into awider, single thickness web before extraction of the plasticizer.

[0121] Although not illustrated, if a sheet die is used, it may bedesirable to pass a resultant three-layer precursor film 30 through thenip of two or more calender rolls to aid in controlling film thicknessand other properties. Alternatively, the hot precursor film 30 may becast onto a quench roll and a series of draw down rolls used to controlfilm thickness and other properties.

[0122] In addition, three-layer precursor film 30, whether formed in ablown film die, as a calendered film from a sheet die and calenderstack, or as a melt cast film from a sheet die and quench roll, can bedrawn in the machine and/or cross machine direction by means of atentering frame to modify film thickness and other properties.

[0123] The three-layer film 30 formed by coextrusion die 20, with orwithout modification by various intermediate processes, is fed alongwith an anode collector 81 and a cathode collector 83 into the nip oflaminating rolls 84 and 85 to form a complete cell structure. Thecurrent collectors in roll stock form are supplied from unwind stations80 and 82 to the laminating rolls.

[0124] A five-layer cell structure 86, which includes three-layerprecursor film 30, is fed around roll 40 and into an extraction bath 42contained in tank 44. The five-layer cell structure then passes around aroll 46 and exits tank 44. The portion of the five-layer cell structure86 comprised of three-layer precursor film 30 has substantially all ofthe contained plasticizer removed by the solvent in extraction bath 42.The extracted five-layer cell structure passes around roll 60 and entersa drying section 88 where the solvent is volatilized.

[0125] The extracted solvent-free five-layer cell structure 89 passesinto a controlled moisture environment 90 where the cell structure iscut to length, cut lengths are assembled into individual batteries,electrolyte is introduced, and other final assembly operations arecarried out. When the cell structure is cut to length, the continuousportion of the battery production ends.

[0126] The extraction process has been illustrated as being carried outin tank 44 for ease of illustration. However, the extraction ispreferably carried out in an extractor similar to that described in U.S.Pat. No. 4,648,417. After extrusion, the resultant multiple layer cellstructure can be further calendered to control porosity and layerthickness. (This is true irrespective of whether current collectors arepresent.)

[0127] The continuously produced multiple (three)-layer cell assembly 30(before extraction) and multiple (five)-layer electrochemical cellstructure 86 are illustrated in FIGS. 4 and 5, respectively. As can beseen, cell structure 86 is comprised of an anode current collector 81,an anode layer 52, a separator layer 54, a cathode layer 56, and acathode current collector 83.

[0128] Although the process of forming the multiple layer cell structureof this invention is preferably accomplished by coextruding the anode,separator, and cathode; laminating current collectors; extracting theplasticizer; and removing the extraction solvent in a continuous seriesof operations, the operations can be performed separately or in variouscombinations. If the anode, separator, and cathode layers are formedseparately, they would preferably be laminated to each other and totheir respective current collectors before solvent extraction of theplasticizer to promote coherent bonding between the adjacent layers.However, it may be desirable to extract the plasticizer from one or moreof these layers in a separate operation and subsequently laminate theextracted layers. If the anode, cathode, and separator layers are formedseparately, it may be desirable to pass the respective extrudate fromeach extruder through a calender roll stack to aid in controlling filmthickness and other parameters. A suitable such calender roll stack isdisclosed in U.S. Pat. No. 4,734,229. After solvent extraction of theplasticizer, the cell assembly is passed into a controlled moistureenvironment, as is well known in the art.

[0129] Whether the anode, cathode, and separator films are formedseparately or as a multiple layer film, the film or films may beoriented (stretched) in the machine direction, cross-machine direction,or both, before or after solvent extraction of the plasticizer from thefilm but prior to lamination to current collectors.

[0130] After the electrochemical cell assembly is formed, the web is cutto size, packaged, and grouped into batteries. The packaged cellassemblies are then filled with electrolyte and sealed, all in a mannerknown in the art.

[0131] The anode precursor of the present invention preferably comprisesa plasticizer, a polymer matrix containing UHMWPE, and a carbonmaterial. Natural or synthetic graphite is a preferred carbon material.Other carbonaceous materials that can be used include carbon black, lampblack, coke, carbon fibers, or mesocarbon, or mixtures thereof. Theanode may also include other minor ingredients.

[0132] The cathode precursor of the present invention preferablycomprises a plasticizer, a polymer matrix containing UHMWPE, and acathode filler, the last of which is a mixture of compounds that willform a cathodic insertion complex with lithium ions and anelectroconductive material. Such cathodic materials are well known inthe art. Examples include: oxides of cobalt, manganese, molybdenum,vanadium, chromium and copper; sulfides of titanium, molybdenum andniobium; lithiated cobalt oxides (e.g., LiCoO₂ and LiCoVO₄); lithiatedmanganese oxides (e.g., LiMn₂O₄); lithiated nickel oxides (e.g., LiNiO₂and LiNiVO₄); and mixtures thereof. Other examples includecathode-active material blends of Li_(x)Mn₂O₄ (spinel) described in U.S.Pat. No. 5,429,890. The blends can include Li_(x)Mn₂O₄ (spinel) and atleast one lithiated metal oxide material selected from Li_(x)NiO₂ andLi_(x)CoO₂ wherein 0<x≦2.

[0133] U.S. Pat. No. 5,778,515 discloses that the cathodic material maybe mixed with an electroconductive material, such as graphite, powderedcarbon, powdered nickel particles, conductive polymers, and the like. Itis preferred to include such an electroconductive material in thecathodes formed in the present invention.

[0134] The separator precursor is formed from a mixture of aplasticizer, a polymer matrix containing UHMWPE, and a filler or fillerssuch as precipitated silica, fumed silica, chemically modifiedprecipitated silica, chemically modified fumed silica, or lithiumphosphate. The preferred filler is fumed hydrophobic silica. Examples ofsuch silicas include Degussa Areosil R812S and J. M. Huber Cab-OsilTS-530.

EXAMPLE 24 Anode Precursor Composition

[0135] A two-part anode precursor composition was prepared by forming asuspension of polymer and plasticizer, and an anode active materialmixture.

[0136] The polymer plasticizer suspension was prepared in a 15 litercylinder, using a Lightning Model Paratrol A mixer, turning at 800 rpm.The components of the suspension consisted of: Shellflex™ 3681naphthenic process oil (2,154.3 g), manufactured by Shell Oil, andMontel 1900H™ UHMWPE (232.5 g), manufactured by Montel. The oil wasadded first, followed by the UHMWPE. After both components were added,mixing continued for ten minutes at ambient temperature. After initialmixing was complete, the mixer speed was maintained at 500 rpm toprevent separation.

[0137] The anode active material mixture was prepared in a LittlefordModel W-10 mixer. The components of the anode active material consistedof: BG-35™ graphite (5,118.5 g), manufactured by Superior Graphite Co.,and Super P™ carbon black (189.2 g), manufactured by MMM Carbon. Thegraphite was added first, followed by the carbon black. Mixing wascarried out at 1,000 rpm for three minutes at ambient temperature. Thefinal anode film composition is determined when the UHMWPE/plasticizersuspension and the anode precursor composition are metered together asin Example 27.

EXAMPLE 25

[0138] Cathode Precursor Composition

[0139] A two-part cathode precursor composition was prepared by forminga suspension of polymer and plasticizer, and a cathode active materialmixture.

[0140] The polymer and plasticizer suspension was prepared in a 15 litercylinder using a Lightning Model Paratrol A mixer, turning at 1,000 rpm.The components of the suspension, in order of addition to the mixercylinder, consisted of: Shellflex™ 3681 naphthenic process oil (3,636g), manufactured by Shell Oil, and Montel 1900H™ UHMWPE (377 g),manufactured by Montel.

[0141] The cathode active material mixture was prepared in a LittlefordModel W-10 mixer. The components of the cathode active material mixture,in the order of addition to the mixer, consisted of: Super P™ carbonblack (954 g), manufactured by MMM, and lithium-manganese oxide powder(11,240.2 g), manufactured by Japan Energy Corporation. After all theingredients were added, mixing continued at 1,000 rpm for three minutesat ambient temperature. The final cathode film composition is determinedwhen the UHMWPE/plasticizer suspension and the cathode precursorcomposition are metered together as in Example 27.

EXAMPLE 26 Separator Precursor Composition

[0142] A separator precursor composition slurry was prepared in a 15liter cylinder using a Lightning Model Paratrol A mixer, turning at 800rpm. The components of the slurry, in order of addition to the mixercylinder, consisted of: Shellflex™ 3681 naphthenic process oil (2,359.6g) manufactured by Shell Oil; Montel 1900H™ UHMWPE (243.6 g)manufactured by Montel; and Aerosil R812S™ hydrophobic fumed silica(312.8 g) manufactured by Degussa. After all the ingredients were added,mixing continued for ten minutes. All mixing was done at ambienttemperature. After initial mixing, the mixer speed was maintained at 500rpm to prevent separation.

EXAMPLE 27 Formation of Individual Films

[0143] The polymer and plasticizer suspension prepared in Example 24 wasmetered into the feed port of a twin screw extruder using a modifiedKtron type K-SFS-24/6 gravimetric feeder, controlling a Cole-ParmerMasterflex Model 77300-50 peristaltic pump. A 15 liter cylinder mountedon the load cell containing the anode slurry supplied the peristalticpump. A Lightning Lab Master Model PH-1 mixer mounted above the cylinderand turning at 500 rpm maintained the slurry in suspension. The polymerand plasticizer suspension was metered into the feed port at a rate of19.4 grams per minute.

[0144] The anode active material mixture prepared in Example 24 wasmetered into a second feed port located 250 mm downstream from theprimary feed port. The anode active material mixture was metered intothe second feed port at a rate of 43 grams per minute using a Ktron typeK-SFS 24/6 gravimetric feeder.

[0145] The extruder was a co-rotating twin screw extruder manufacturedby Betol Machinery LTD, which had a barrel diameter of 40 mm and alength to diameter ratio of 30:1. The extruder barrel temperature was180° C., the screw speed was 46 rpm, and the extruder residence time wasfour minutes.

[0146] The extrudate from the extruder was fed into a sheet die with awidth of 40 mm and a die opening of 0.1 mm. The sheet issuing from thedie was cut into pieces 60 mm long.

[0147] The procedure was repeated for the polymer and plasticizersuspension and cathode active material mixture prepared in Example 25with the exception that the polymer and plasticizer suspension wasmetered at 33.7 grams per minute, the cathode active material mixturewas metered at 93.1 grams per minute, the extruder screw speed was 69rpm, and the die opening was 0.15 mm.

[0148] The procedure was also repeated for the separator slurry preparedin Example 26 with the exception that the separator slurry was meteredinto the first extruder feed port at 24.7 grams per minute, the secondfeed port was closed, the extruder screw speed was 30 rpm, the dieopening was 0.05 mm, and the sheet issuing from the die was cut intopieces 80 mm long.

EXAMPLE 28 Formation of a Cell Assembly

[0149] An anode collector was made in the form of an 80 mm×40 mmrectangle cut from a 0.04 mm thick MicroGrid™ expanded copper foil, madeby Delker Corporation under Part No. 1.5Cu6-077F.

[0150] A cathode collector was made in the form of an 80 mm×40 mmrectangle cut from a 0.05 mm thick MicroGrid™ expanded aluminum foilmade by Delker Corporation under Part No. 2A16-077F.

[0151] A lay up for the multiple layer cell assembly was formed bylaying the anode sheet formed in Example 27 on top of the anodecollector, such that a 20 mm×40 mm portion of the collector was leftuncovered to serve as a current lug. The separator sheet formed inExample 27 was laid on top of the anode sheet so that the separatorsheet overlapped the anode sheet evenly on all sides. The cathode sheetformed in Example 27 was laid on top of the separator sheet such thatthe separator sheet overlapped the cathode sheet evenly on all sides.The cathode collector was laid on top of the cathode sheet such that a20 mm×40 mm portion of the collector was left uncovered to serve as acurrent lug. The multiple layer cell thus laid up was laminated in aModel C Carver Lab Press at a pressure of 2 psi and at a temperature of250° C. for 60 seconds.

[0152] The laminated cell assembly was extracted under a hood in 500 mlof trichloroethylene at ambient temperature for twenty minutes. Afterthe cell assembly was removed from the extraction solvent, the residualtrichloroethylene was allowed to evaporate under a hood at ambienttemperature for one hour. The plasticizer remaining after extraction wasabout 7% by weight of the multiple layer cell assembly, not includingthe current collectors. Current leads were supplied in the form ofstainless steel wires spot welded to each current lug.

[0153] The extracted multiple layer cell assembly was dried at 60° C.for six hours and transferred to a glove box purged with dry nitrogen.The cell assembly was allowed to freely imbibe an electrolyte consistingof a 1 mol/L solution of lithium hexafluorophosphate in a 50:50 byvolume mixture of dimethyl carbonate and ethylene carbonate. Theelectrolyte saturated cell assembly was placed in a Mylar pouch with thecurrent leads extending outside the pouch. The pouch was made gas tightby heat sealing the open side of the couch over the current leads.

[0154] This cell was removed from the glove box, and the anode collectortab was connected to the negative terminal of a Hewlett Packard Model6611C DC power supply. The cathode collector tab was connected to thepositive terminal by similar means. The power supply voltage limit wasset to 4.2 volts, and the current limit was set to 0.0121 ampere. Theon-charge cell voltage gradually increased to 4.2 volts after 3.93hours. The charging current gradually decreased, and charging wasterminated at approximately 0.0005 ampere. The cell was discharged at0.0121 ampere to a cut off voltage of 2.7 volts. The cell performancewas similar to that of Example 21, Table 4.

[0155] It will be obvious to those having skill in the art that manychanges may be made to the details of the above-described embodiments ofthis invention without departing from the underlying principles thereof.The scope of the present invention should, therefore, be determined onlyby the following claims.

1. A coextrusion process for simultaneously producting a unitaryelectrode assembly composed of anode, cathode, and separator layersformed as a multiple layer web, comprising: introducing into an anode anultrahigh molecular weight polyolefin, a plasticizer, and an anodeactive material to form an anode extrudate layer; introducing into acathode extruder an ulrahigh molecular weight polyolefin, a plasticizer,and a cathode active material to form a cathode extrudate layer;introducing into a separator extruder an ultrahigh molecular weightpolyolefin, a plasticizer, and an electrically nonconductive materialfiller to form a separator extrudate layer; and forming a coherent bondbetween adjacent ones of the anode, cathode, and separator extrudatelayers to form a multiple layer web in which the separator extrudatelayer is positioned between anode and cathode extrudate layers.
 2. Themethod of claim 1, in which the forming of a coherent bond comprisescoextruding the anode, cathode, and separator extrudate layers.
 3. Themethod of claim 1, in which the forming of a coherent bond compriseslaminating together the anode, cathode, and separator extrudate layers.4. The method of claim 1, further comprising bonding a different one ofa pair of current collector layers to each of the anode extrudate layerand the cathode extrudate layer to form an electrochemical cell.